Would a covert tender dock submarines below the surface?

Would below-surface docking be useful for a covert submarine tender?

Probably not; it adds extreme engineering difficulty before surveillance makes submerged docking worth the cost.

A below-surface docking tender is an impractical answer to a problem that navies do not yet face. Satellites are unlikely to appear earlier, so a conventional tender can support submarines in remote waters without needing a vast moon pool. Germany might disguise a merchant support ship, but docking a submarine inside it at sea would impose severe size, stability, and handling problems. The simpler surface arrangement offers enough concealment and support for the period.